The use of conversion tables in musical inventions is well known. The Korg i-3 auto-accompaniment keyboard is one example of a product employing such tables. Like other auto-accompaniment type keyboards, the Korg i-3 performs chord analysis on the notes played by the user in a control area of the keyboard, determines a chord for the input notes, and selects a conversion table from a plurality of stored conversion tables, stored in the keyboard's electronic memory, so as to conform the resultant output notes to a predetermined chord. For example, a look-up table can be utilized in this fashion, which takes selected notes in a given chord as inputs and generates output notes that are within a scale corresponding to the input chord. The conversion table is thus used to transpose the notes of input musical material, in real-time, into a different output key or tonality.
Typically, the above conversion tables are provided for only 10-20 chords, with each of the conversion tables having fixed values. Memory requirements and the time-consuming operations of creating, testing, and maintaining these tables typically preclude a greater number of chord types from being made available. However, thousands of input chords are possible within music when all of the different scale tones which may be added to traditionally recognized chords are considered. Some of these additional tones are referred to as tensions, examples of which are a flat ninth (.music-flat.9), a ninth (9th), a sharp ninth (.music-sharp.9), an eleventh (11) a sharp eleventh (.music-sharp.11), a thirteenth (13), and a flat thirteenth (.music-flat.13). Many of these tensions can be combined within the same chord. Thus, having a conversion table for each chord and combination of tensions is both memory intensive and difficult to manage.
Another disadvantage of prior art table lookup methods is that predetermined decisions are made as to which notes are valid for a given chord, including tension types. Occasionally, the user may wish to allow "non-chordal" tones (i.e. tones not within the chord or scale or which are not considered to be valid tensions). For example, the chord CMaj7 typically has no provision for allowing an A.music-sharp. to be present in the scale. In such prior art methods, the presence of the A.music-sharp. is generally not acknowledged, and there is no way for the user to obtain an A.music-sharp. in the resulting output material even if desired, since no provisions are made for it in a conversion table.
Conversion tables are not limited to being used to constrain pitches to desired chord types or scales. U.S. Pat. No. 5,521,327, issued to Kay ct al., shows means for selectively changing drum notes to other drum notes using a plurality of fixed conversion tables, often referred to as conversion maps. However, if the number of drum notes to be changed is very large, the size of each table grows, thereby increasing the number of desired conversion maps, the number of drum notes, table memory usage and overall table maintenance complexity.